Treatment of diseases and ailments of the body often benefit from short- or long-term infusion of drugs and/or other fluids. While such therapeutic substances may be administered extracorporeally, e.g., via transcutaneous injection, many patient benefit from the consistent and repeatable dosage provided by an implantable infusion device. Such devices may be used in a variety of applications such as control of pain and/or spasticity. They are well-suited to deliver infusate fluids to a targeted delivery site such as an epidural or intrathecal space of the spinal canal, or a particular location within the brain.
Implantable infusion devices are typically implanted subcutaneously, e.g., in the chest or abdominal cavity. The device may incorporate a reservoir to hold the infusate fluid. A self-sealing, needle-penetrable septum may also be provided and is preferably located generally directly beneath the skin. The septum provides a refill port connected to a fluid passageway that permits the reservoir to be refilled periodically via transcutaneous injection. Accordingly, the reservoir can be aspirated and/or filled/refilled without requiring surgical removal from the patient's body, and further without requiring any other significant surgical procedure.
One potential problem with refilling the reservoir of some infusion devices is the potential for reservoir overfilling. Overfilling may lead to over-pressurization of the reservoir, which may cause damage to the components of the device and potentially result in other adverse consequences, e.g., over-infusion to the patient.
In some configurations, a clinician refilling the device with a syringe may rely upon tactile syringe resistance (e.g., pressure-based detection) to sense that the drug reservoir has been filled to capacity. While acceptable in some circumstances, inherent clinician variability may still result in over (or under)—filling. Moreover, while pressure-based systems are useful with some reservoir configurations (e.g., those using a bellows), such pressure-based solutions are not easily adaptable to devices incorporating flexible, ambient pressure reservoirs.
In other infusion devices, a pin may be mechanically coupled to a closed end of the reservoir such that a head of the pin seats to seal off the fluid passageway from the reservoir once the latter is at or near full capacity. While effective, devices incorporating such valve configurations may require a certain level of expertise to refill. For example, with the pin seated, aspiration of the reservoir may require the clinician to establish a sustained syringe vacuum pressure while the fluid slowly leaks around the pin and releases it from its valve seat.
Yet another potential problem with aspirating/refilling infusion devices concerns clinician feedback regarding needle position and fluid volume within the reservoir. For example, it may be difficult with some device configurations to determine whether the needle is fully and correctly located within the septum of the device. Accordingly, outside of tactile feedback detectable at the syringe, it may be difficult for less-experienced clinicians to initially determine whether the syringe fluid is being delivered into the reservoir or to an area outside of the device.